Molten lava once covered Mercury’s vast northern volcanic plains. Lava nearly filled the 181-mile-wide (291 km) Mendelssohn impact basin, which lies at the lower right of this enhanced-color image. As the lava cooled, it formed large ridges that appear particularly prominent at bottom left. Meanwhile, the bright orange region near the scene’s top shows the location of a volcanic vent that unleashed one of the planet’s largest pyroclastic flows.